1. Field of the Invention
This invention relates generally to athletic shoes, and more particularly to systems for cushioning the midsoles of athletic shoes.
2. Description of Related Art
In recent years, there have been a number of attempts to incorporate additional cushioning into the midsole of an athletic shoe. The midsole of a shoe is the portion of the shoe which lies between the outsole and the inner sole and it is the development of the midsole which has led to shoes which take into account human foot physiology. It is the midsole of the shoe, usually made of a polyurethane or ethylene vinyl acetate (EVA) material, which is primarily designed to manage pronation problems and to absorb shock.
One category of developments which attempt to cushion the foot of a user is those which incorporate a pneumatic device within the midsole. This concept is shown in U.S. Pat. No. 545,705, issued to MacDonald. In this patent, an elastic air-filled cushioning device is incorporated into the heel of a shoe to provide cushioning. A similar device is taught in U.S. Pat. No. 1,498,838 issued to Harrison, Jr., which utilizes a number of tubes which lie within the midsole of a shoe. These tubes are inflated by a valve to maintain a pressure above ambient pressure. The tubes in Harrison, Jr., are made of a flexible material which is inelastic. Another patent in this same category is U.S. Pat. No. 4,219,945, issued to Rudy, which discloses a pneumatically inflated insert which is encapsulated in a foam midsole. In the shoe taught by this patent, the insert is filled with a mixture of large-molecule gases which attempts to prevent diffusion outwardly from the chambered insert.
The disadvantages of encapsulating gas within the midsole of a shoe are numerous. It is exceedingly difficult and costly to encapsulate gas in a material which also has desirable mechanical properties. It is much easier, for example, to cut a piece of EVA to desired specifications than to make a container which retains pressurized air or other gas. Many easily molded plastics will allow encapsulated air to diffuse out of its container. Therefore, large molecule gases must be used as the encapsulated gas thereby increasing the expense of manufacturing such a shoe. Material puncture is also a problem with pressurized gas midsoles.
Another serious drawback with shoes utilizing a pressurized encapsulated midsole is that the pressure of the gas within the escapsulating container is temperature dependent. As a shoe warms up, it has a different stiffness. Similarly, the shoe may respond differently in warm or cold temperature. The response of these types of midsoles may also be altitude dependent.
Yet another serious drawback in the encapsulated gas midsoles of the prior art is that these shoes do not have adequate rearfoot control and stability. In simple terms, encapsulated gas midsoles are often times too mushy to give proper support.
In addition to the three patents discussed above, there are a number of other patents which attempt to cushion the midsole of a shoe by using a pneumatic insert. Many of these devices have the same disadvantages, e.g., requiring that the tubes maintain their inflated pressure, diffusion through the tubes, and manufacturing difficulties.
Another category of development which attempts to provide extra cushioning to the midsole of a shoe is disclosed in U.S. Pat. No. 4,322,892 issued to Inohara, which teaches a shoe having a wedge portion which forms the heel of the shoe. This wedge portion has incorporated therein a number of hexagon-shaped apertures which traverse the width of the shoe. This patent also discloses the possibility of using circular cylinders rather than hexagonal apertures. Because the apertures are merely voids formed directly in the midsole, the shoe taught by this patent does not achieve rebound and cushioning to the extent possible. U.S. Pat. No. 4,235,026, issued to Plagenhoef, shows a midsole of a shoe which utilizes triangular openings. These openings extend from the lateral side of a shoe but do not extend completely through the shoe. This allows greater cushioning at the portion of the foot which first impacts the ground and less cushioning at the medial side of the shoe. This shoe seeks to account for the fact that the lateral side of a shoe strikes the ground first and the foot rolls in the direction of the medial side of the shoe. U.S. Pat. No. 4,445,284, issued to Sakutori, shows a shoe which has bores which traverse the shoe in a direction perpendicular to the longitudinal axis of the shoe. These bores have at each end thereof a check valve which allows air to flow into the longitudinal bores but not out of the longitudinal bores. Also communicating with each bore is a narrow slot which enables air to flow out of the bore upon compression of the bore. Another patent which uses air at ambient pressure within circular bores is U.S. Pat. No. 4,593,482, issued to Mayer, which shows a sandal having a plurality of interconnecting modular elements. These modular elements form the sole of a shoe and are closely packed. U.S. Pat. No. 4,656,760, issued to Tonkel et al., is a cellular insert for a midsole of a shoe. While in one embodiment of this invention the cells formed by a polymeric woven material form hollow cells, these cells are formed from a single strand of material and therefore cannot act independently of each.
U.S. Pat. No. 4,430,810, issued to Bente, discloses a shoe which utilizes at least one replaceable insert in the sole of a shoe. The tubes in this shoe are made to frictionally engage a bore in the midsole of the shoe, thereby causing localized pressure differentials and gradients in the surrounding material. The Bente patent is directed to a device for controlling the stiffness of a shoe and is therefore able to use solid rod inserts.
U.S. Pat. No. 4,536,974, issued to Cohen, is a shoe with a deflective and compressible midsole. This shoe utilizes a plurality of ribs which, when a force is applied to the midsole, deflect and come into contact thereby restricting further deflection. There are two separate and distinct compression stages in the Cohen midsole. Initially, the ribs in Cohen do not easily deflect. As the midsole compresses, it becomes increasingly less difficult to compress the midsole. Therefore, in the first stage of compression there is a negative pressure gradient, that is, the greater the deflection, the less force needed to deflect. In the second compression stage of Cohen, the ribs come into contact with each other. When the ribs are in contact, the only way for the midsole to compress is for the ribs to compress. Therefore, in the second stage of compression there is a positive pressure gradient; the more the midsole is compressed the greater force is needed to compress. In the Cohen device there may also be secondary buckling of the ribs because the forces are not angled along the rib.
It is clear from the developments discussed above that there are many disadvantages in the art related to the present invention. The disadvantages of encapsulated gas soles include high construction costs, lack of stability, puncture problems, temperature dependence, and diffusion of gas out of the gas container. For other soles having various apertures, the disadvantages include abrupt changes in the pressure needed to deflect the midsole. Other shoes simply have not recognized the need to provide a sole having good rebound as well as cushioning.
One of the trends in athletic footwear is to present the technology of the footwear in such a fashion as to enable the purchaser to visualize the technology. Unfortunately, it can be difficult to display the technology without adversely affecting the performance of the shoe. For example, some shoes have provided "windows" for viewing the interior of midsoles. Such windows, placed on the edge of the midsole, may effect the cushioning characteristics of the midsole. If such is the case, displaying the technology may outweigh whatever benefits may be derived from the technology itself.
One of the objects of the invention is to provide a way of viewing the invention in a useful and unobtrusive way.